1904. =imperii= (_Putorius arcticus_) Barrett-Hamilton [= _Mustela erminea richardsonii_], Ann. and Mag. Nat. Hist., ser. 7, 13:392, May, 1904, based on an animal from Fort Simpson, Mackenzie, Canada, proves to be inseparable from _richardsonii_ which has priority.
1904. =polaris= (_Putorius arcticus_) Barrett-Hamilton [= _Mustela erminea polaris_], Ann. and Mag. Nat. Hist., ser. 7, 13:393, May, 1904, is the name used for the ermine of eastern Greenland and since 1945 has been used for the weasel of Greenland as a whole.
1905. =macrophonius= (_Putorius_) Elliott [= _Mustela frenata macrophonius_], Proc. Biol. Soc. Washington, 18:235, December 9, 1905, applies to the long-tailed weasel of the mountains along the eastern border of Veracruz.
1906. =leptus= (_Putorius streatori_) Merriam [= _Mustela erminea murica_], Proc. Biol. Soc. Washington, 16:76, May 29, 1903, until 1945 was applied to the diminutive ermine of the Rocky Mountains from Wyoming south to northern New Mexico but proves to be a synonym of _muricus_ with type locality in the Sierra Nevada of California.
1908. =angustidens= (_Putorius cicognanii_) Brown [= _Mustela erminea angustidens_], Mem. Amer. Mus. Nat. Hist., 9(pt. 4):181, pl. 17, is applied to an extinct subspecies known from fossil remains of Pleistocene age from northern Arkansas.
1908. =gracilis= (_Putorius_) Brown [= _Mustela frenata gracilis_], Mem. Amer. Mus. Nat. Hist., 9(pt. 4):182, 1908, applies to a Pleistocene weasel known from a single skull from northern Arkansas.
1912. =costaricensis= (_Mustela_) Goldman [= _Mustela frenata costaricensis_], Proc. Biol. Soc. Washington, 25:9, January 23, 1912, applies to the long-tailed weasel of Costa Rica.
1913. =primulina= (_Mustela_) Jackson [= _Mustela frenata primulina_], Proc. Biol. Soc. Washington, 26:123, May 21, 1913, applies to the long-tailed weasel of the central part of the United States in eastern Kansas and adjoining areas.
1913. =campestris= (_Mustela_) Jackson [= _Mustela rixosa campestris_], Proc. Biol. Soc. Washington, 26:124, May 21, 1913, applies to the least weasel of the Great Plains region.
1913. =olivacea= (_Mustela peninsulae_) Howell [= _Mustela frenata olivacea_], Proc. Biol. Soc. Washington, 26:139, May 21, 1913, applies to the long-tailed weasel of the southeastern United States excepting most of Florida.